The present invention, in some embodiments thereof, relates to inkjet printing and, more particularly, but not exclusively, to dye discharge compositions and uses thereof in inkjet printing.
Dye discharge printing, also known as extract printing, is a method of forming a design onto a dyed substrate, typically a fabric, by printing thereon a color-destroying (dye discharging) agent, such as chlorine or hydrosulfite, to bleach out a light pattern on to the darker colored substrate. In color-discharge printing, a dye or pigment, which is impervious to the discharging agent, may be combined with the reducing (discharge) agent so as to color the discharged part of the substrate thereby imparting a colored design instead of dye-free areas on the substrate.
Discharge printing has the ability to make bright, opaque colors on dark fabrics, while keeping the substrate's surface smooth and allowing the finished fabric to exhibit a soft hand-feel owing to the fact that substance is withdrawn rather than added to the fabric in the printing process.
Newly developed discharge ink systems involve highly reactive chemicals that are typically derived from stable compounds by decomposition at high temperature. This advancement opened the door to discharge printing for the standard screen (stencil) printing techniques.
Successful light-on-dark printing with standard inks relies on a white background silhouette or a white underbase layer, increased pigment loads, fillers and other additives to block out the color of the substrate. Discharge inks modify the garment color by removing the substrate's original color and optionally replacing it with the new ink color.
One of the most promising technologies for printing high quality color designs and images, particularly in small batches of varying contents (short runs of variable data), on a wide variety of types and shapes of substrates, such as textile surfaces, is inkjet printing. Inkjet printing is a wide-spread technique in which a stream of a specific liquid ink composition is ejected as droplets from a cluster of minute nozzles (printheads) in response to electrical signals generated by a microprocessor to record characters and patterns on the surface of a printing subject without making direct contact between the ink application apparatus and the surface of the subject (non-impact printing). A typical inkjet printing system includes methods and apparatus in which electric signals are converted to mechanical signals for a continuous or on-demand jetting of an ink composition which is continuously supplied and stored in a nozzle head portion, to thereby record characters, symbols and patterns on the surface of a subject.
Dye discharge ink compositions are typically suitable for screen printing, and are less suitable for inkjet settings, due to, for example, incompatible high viscosity, incompatible particulate matter, corrosive aptitude, and chemical and physical instability, which leads to decomposition and sedimentation and hence short shelf life of the ink composition.
Texcharge® TC by Sericol® is a water-based discharge ink system, designed to provide maximum opacity and impact when printed on reactive dyed cottons. This system is designed for the silk or screen printing technologies, namely the compositions are thick or pasty, allowing them to pass through the mesh without feathering under masked areas.
U.S. Patent Application having publication No. 20080250967 teaches a dye discharging ink for inkjet printing which includes a reducing agent and an amine compound, wherein the reducing agent is a sulfur reducing agent such as Rongalite, and, the amine compound is an alcohol amine compound such as triethanolamine. The dye discharging ink taught therein also includes a surface active surfactant and/or a corrosion inhibitor, and the pH of the ink composition ranges from 9.5 to 11.0 so as to minimize corrosion of head nozzles due to acidic substances produced by decomposition of a reducing agent, and so as to decrease inhibition of linear advancing property of ejected ink.
The presently available ink compositions, including compositions that are suitable for inkjet printing, include aqueous-based ink compositions and non-aqueous solvent-based ink compositions. The more commonly used inkjet compositions are aqueous-based ink compositions, which typically include water and a colorant, usually a dye or pigment dispersion, and may further contain a number of additives for imparting certain attributes to the ink as it is being applied (jetted), e.g., improved stability and flow, anti-corrosiveness, and feather and bleeding resistance), as well as attributes to affect its final cured properties such as improved adhesion to the substrate (e.g., the capability to form chemical bonds with the substrate), flexibility, stretchability, softness and the like.
To ensure high quality images by inkjet, the ink composition should be characterized by free passage through the nozzles, minimal bleeding, paddling and/or smearing, uniform printing on the surface of the subject, wash-fastness, simple system cleaning and other chemical and physical characteristics. Thus, inkjet ink compositions characterized, for example, by extended chemical and physical stability, suitable viscosity, solubility, volatility, surface tension, compatibility with other components of the printing system and, in cases of continuous flow inkjet printing, electrical resistance, and further by being applied using suitable apparati, techniques and processes, are continuously sought for.
In case of printed fabrics (e.g., printed garments), in order to sustain wear and tear due to frequent use and wash cycles, the printed image on the final product, as well as the final product itself, should exhibit the properties of an elastic yet aerated film, and therefore the printed layer imparted on the substrate at the end of the printing process should be minimal, and the ink composition should also contain components which can impart such compressibility (softness), plasticity, elasticity, flexibility and stretchability.
U.S. Pat. No. 7,134,749, by the present assignee, which is incorporated by reference as if fully set forth herein, teaches a method and apparatus for color printing on a dark textile piece. IL Patent No. 162231 and WO 2005/115089, by the present assignee, which are incorporated by reference as if fully set forth herein, teach processes and systems for printing high quality, high resolution, multi-color images on fibrous or porous materials or other ink absorbing materials, or on materials having high surface tension with the ink liquid, and especially over garments, effected by applying a wetting composition prior to applying an ink composition and formation of the images.
U.S. Patent Application having Publication Nos. 20070103528 and 20070104899, by the present assignee, which are incorporated by reference as if fully set forth herein, teach individual and integrated processes, methods and compositions for printing high quality, high resolution, multi-color images on lightly and/or darkly colored fibrous or porous materials or other ink absorbing materials, which also provide a mechanism for drop immobilization aimed at inhibiting the adsorption by fabric, the bleeding, smearing, paddling and feathering of the jetted ink droplets.
U.S. Patent Application having Publication No. 2011/0032304 (recently allowed), by the present assignee, which is incorporated by reference as if fully set forth herein, teach multi-part ink compositions and integrated processes for printing high-quality and physically durable and serviceable color images on various dark or light-colored surfaces, including absorptive and non-absorptive substrates, which are especially suitable for inkjet printing on stretchable, flexible and bendable materials, and utilize inter-reactive agents which are capable of interacting upon contact therebetween on the surface of the substrate so as to effect immobilization of the liquid ink composition.